Ferrimagnetic material capable of sustaining magnetostatic waves (MSW) have been used for fabricating resonator devices. In the prior art, solid yttrium iron garnet (YIG), both spheres and slabs, have been found to be resonant under certain conditions, and this fact has encouraged the use of YIG films for ferrimagnetic material in MSW resonator devices. For example, J. D. Adam in "Delay of Magnetostatic Surface Waves in Y.I.G. Slab", Electronics Letters, Vol. 6, No. 22 (1970) and L. K. Brundle et al, in "Magnetostatic Surface Waves on a Y.I.G. Slab," Electronics Letters, Vol. 4, No. 7 (1968) discuss resonance of YIG slabs; and J. P. Castera et al. In "Magnetostatic Wave Resonators," Proc. of 1981 RADC, 218-228 (1981) discuss resonance of YIG thin film devices. In these prior art MSW thin film resonator devices, complex array reflectors are required to be formed on the films as resonant cavities for the device. Such complex array reflectors usually are patterned with mask and etch techniques on the YIG film, or they are formed in the film by ion-implantation. Neither an etch technique nor an ion-implantation technique in the fabrication of a MSW resonator device is considered simple or economical.
In accordance with the preferred embodiment of the invention, a YIG film is formed with two straight and substantially parallel edges on a substrate. These simple substantially parallel edges, which act as reflectors, constitute the resonant cavity of the device and obviate the required complex and expensive construction of array reflectors of the prior art. Furthermore, because of the planar structure of the resonant cavity, less space and less volume of magnetic field are required than for prior art YIG spheres, which require three-dimensional, and hence more voluminous, cavities.